Die-casting apparatus for fabricating vehicle part casing and method of fabricating vehicle part casing using the same

ABSTRACT

A method of fabricating a vehicle part casing using a die-casting apparatus includes preparing a molten aluminum (AL) alloy by heating an Al alloy. A die-casting mold is preheated, and then, the vehicle part casing is molded by pouring the molten Al alloy into the die-casting mold. The vehicle part casing is removed from the die-casting mold and a surface of the vehicle part casing is trimmed. Burs on the vehicle part casing are removed.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims the benefit of priority to Korean PatentApplication No. 10-2015-0171950 filed on Dec. 4, 2015, the entirecontent of which is incorporated herein for all purposes by thisreference.

TECHNICAL FIELD

The present disclosure relates to a die-casting apparatus forfabricating a casing and a method of fabricating the casing using thesame. More particularly, the present disclosure relates to a die-castingapparatus for fabricating a vehicle part casing and a method offabricating a vehicle part casing using the same, in which a casing fora vehicle part or a machine part is fabricated from aluminum using adie-casting process.

BACKGROUND

In general, casting refers to a process of solidifying metal into acertain shape by pouring metal into a mold, and a product formed throughthis process is referred to as a cast-iron product. Casting technologyis one of the most basic metal machining technologies and important inthe development of the metal industry.

Casting technology is closely related to and has been used in thevehicle industry to the extent that about 50% of cast-iron productsfabricated by the casting technology are used in vehicles.

Recently, light weight vehicle bodies are desirable in order to reduceexhaust due to environmental regulations and improve fuel efficiency. Inthis regard, research into aluminum (Al) alloy materials, in whichenvironmental friendliness, high functionality, light weight, highsensitivity, and the like are considered, have been actively undertaken.

In particular, there exists a need to develop technologies forfabricating a vehicle part casing using an Al material. Vehicle partcasings, a major component of a vehicle, are typically heavy parts. Inaddition, it is required to develop a vehicle part casing formaintaining the structural strength of existing products while beinglight-weighted.

Recently, active researches and development have been undertaken inorder to fabricate vehicle part casings using Al alloy die-castingtechnology, which fabricates Al alloy products by pouring a molten Alalloy, in which Cu, Si, Mg, Ni, and the like are added to the majorcomponent of Al, at a high pressure into a metal mold.

However, Al die-casting molds of the related art have a limited abilityto exhaust gas contained in a molten Al alloy in the process ofdie-casting a vehicle part casing having a complicated shape. Inaddition, voids are formed in a product, which reduces structuralstrength of the product, thus, deteriorating productivity.

The information disclosed in the Background of the Invention section isonly for the enhancement of understanding of the background of theinvention, and should not be taken as an acknowledgment or as any formof suggestion that this information forms a prior art that would alreadybe known to a person skilled in the art.

SUMMARY

The present disclosure has been made keeping in mind the above problemsoccurring in the related art. An aspect of the present disclosureprovides a die-casting apparatus for fabricating a vehicle part casingcapable of improving the ability to pour a molten metal into a mold andreducing a period of time for cooling products, thereby improvingworkability of products, and a method of fabricating a vehicle partcasing using the same.

Another aspect of the present disclosure provides a die-castingapparatus for fabricating a vehicle part casing capable of maintainingdie-casting conditions due to flowing characteristics of an Al alloy,thereby improving denseness of products and reducing a defective rate ofproducts, and a method of fabricating a vehicle part casing using thesame.

Another aspect of the present disclosure provides a die-castingapparatus for fabricating a vehicle part casing capable of reducing theweight of an Al alloy and improving supporting strength thereof, and amethod of fabricating a vehicle part casing using the same.

Another aspect of the present disclosure provides a die-castingapparatus for fabricating a vehicle part casing capable of improvingability to exhaust gas contained in a molten Al alloy and reducing theamount of gas residing in a cavity in order to reduce voids formed indie-cast products, thereby improving fabrication efficiency, and amethod of fabricating a vehicle part casing using the same.

According to an exemplary embodiment in the present disclosure, a methodof fabricating the vehicle part casing using a die-casting apparatusincludes: preparing a molten aluminum (Al) alloy by heating an Al alloy;preheating a die-casting mold; molding a vehicle part casing by pouringthe molten Al alloy into the die-casting mold; removing the vehicle partcasing from the die-casting mold and trimming a surface of the vehiclepart casing; and removing burs on the vehicle part casing.

The step of preparing the molten Al alloy may include heating the Alalloy at a temperature ranging from 645° C. to 665° C.

The step of preheating the die-casting mold may include preheating thedie-casting mold at a temperature ranging from 220° C. to 250° C.

The step of pouring the molten Al alloy into the die-casting mold mayinclude pouring the molten Al alloy to a lower part of the die-castingmold.

The step of pouring the molten Al alloy into the die-casting mold mayinclude pouring the molten Al alloy at a pressure ranging from 90 MPa to110 MPa while maintaining an internal vacuum pressure of a cavity in thedie-casting mold in a range from 140 mbar to 160 mbar.

The composition of the Al alloy may include 88.2% to 80.3% Al, 9.6% to12.0% Si, 1.5% to 3.5% Cu, 0.1% to 0.5% Mn, 0.1% to 0.3% Mg, 0.1% to0.5% Ni, 0.1% to 0.9% Fe, 0.1% to 0.5% Ti, 0.1% to 1.0% Zn, 0.1% to 0.3%Sn, 0.0% to 0.1% Pb, 0.0% to 0.1% Cr, and inevitable impurities, basedon 100% by weight of the alloy composition.

The step of pouring the molten Al alloy into the die-casting mold mayinclude molding the vehicle part casing while exhausting gas from themolten Al alloy using vacuum.

According to another exemplary embodiment in the present disclosure, adie-casting apparatus for fabricating a vehicle part casing includes: afixed mold having a negative shape so that one side of the vehicle partcasing is carved thereinto; and a movable mold disposed movable in adirection towards the fixed mold, and having a positive shape so thatanother side of the vehicle part casing is carved in relief. The movablemold is engaged with the fixed mold between which a cavity having ashape of the vehicle part casing is formed. An exhausting part isconnected to the cavity and decreases an internal pressure of thecavity. The exhausting part exhausts gas contained in the molten Alalloy that is inserted into the cavity.

The movable mold may include a molten metal path connected to a lowerpart of the cavity, in which a molten metal enters the cavity throughthe molten metal path. A plurality of first gas outlets are formed in anupper part of the cavity, in which the gas is contained in the pluralityof first gas outlets. A plurality of second gas outlets are connected tothe exhausting part to form a vacuum in an interior of the cavity.

The movable mold may have: first gas paths; and second gas pathsconnecting the plurality of first gas outlets and the plurality ofsecond gas outlets to the cavity. A diameter of each of the second gaspaths is smaller than that of the first gas paths.

The die-casting apparatus may further include a pressure sensorconnected to one first gas outlet among the plurality of first gasoutlets to measure an internal pressure of the cavity.

The die-casting apparatus may further include a sleeve part connected tothe molten metal path through which the molten metal is poured. Thesleeve part has a gas outlet in an upper part to exhaust the gastherefrom.

As set forth above, the present disclosure is directed to preheating thedie-casting mold after melting an Al alloy. It is thereby possible toimprove the ability to pour molten metal into a mold and to reduce aperiod of time for cooling products, thereby improving workability ofproducts.

In addition, each of the temperature of the molten Al alloy and thepreheating temperature of the die-casting mold is limited to apredetermined temperature range before the molten Al alloy is pouredinto the cavity. Thus, it is possible to maintain die-casting conditionsdue to flowing characteristics of the Al alloy, thereby improvingdenseness of fabricated vehicle part casings and reducing a defectiverate thereof.

Furthermore, in the Al alloy, the content of Al is reduced, the contentof Si is increased, and a small amount of Ni, Ti, Sn, or Cr is added. Itis therefore possible to reduce the weight of the Al alloy and improvesupporting strength thereof.

In addition, the die-casting mold is implemented as a vacuum die-castingmold. It is therefore possible to exhaust gas contained in the molten Alalloy and reduce the amount of gas residing in the cavity in order toreduce voids formed in die-cast products, thereby improving fabricationefficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be more clearly understood from the following detaileddescription when taken in conjunction with the accompanying drawings.

FIG. 1 is a side-elevation view illustrating a die-casting apparatus forfabricating a vehicle part casing according to an embodiment in thepresent disclosure.

FIG. 2 is a view illustrating a fixed mold according to an embodiment inthe present disclosure.

FIG. 3 is a view illustrating a movable mold according to an embodimentin the present disclosure.

FIG. 4 is a view illustrating a die-casting apparatus for fabricating avehicle part casing according to an embodiment in the presentdisclosure.

FIG. 5 is a view illustrating a sleeve part according to an embodimentin the present disclosure.

FIG. 6 is a flowchart illustrating a method of fabricating a vehiclepart casing using a die-casting apparatus according to an embodiment ofthe present disclosure.

FIGS. 7A-7F are a series of images illustrating defects formed when avehicle part casing was fabricated using molten Al having a temperaturebelow 645° C.

FIG. 8 is an image illustrating defects formed when a vehicle partcasing was fabricated using molten Al having a temperature above 665° C.

FIGS. 9A and 9B are a series of images illustrating a fractured surfaceof a vehicle part casing fabricated according to an example in thepresent disclosure.

FIG. 10 is an image illustrating surface voids formed when a vehiclepart casing was fabricated using a die-casting mold preheated to atemperature below 220° C. according to an example in the presentdisclosure.

FIG. 11 is an image illustrating hit checks formed in a die-casting moldpreheated to a temperature above 250° C. according to an example in thepresent disclosure.

FIG. 12 is an image illustrating shrinkage defects when a vehicle partcasing was fabricated using a die-casting mold preheated to atemperature above 250° C. according to an example in the presentdisclosure.

DETAILED DESCRIPTION

Reference will now be made in greater detail to exemplary embodiments inthe present disclosure, examples of which are illustrated in theaccompanying drawings. However, it should be understood that the presentdisclosure is by no means limited to or restricted by the embodiments.Wherever possible, the same reference numerals will be used throughoutthe drawings and the description to refer to the same or like parts. Inthis manner, the components illustrated in different figures anddescriptions thereof may be referred to. Descriptions of some featureswell-known to a person skilled in the art or repeated descriptions ofsome features may be omitted.

FIG. 1 is a side-elevation view illustrating a die-casting apparatus forfabricating a vehicle part casing according to an embodiment in thepresent disclosure, FIG. 2 is a view illustrating a fixed mold accordingto an embodiment in the present disclosure, FIG. 3 is a viewillustrating a movable mold according to an embodiment in the presentdisclosure, and FIG. 4 is a view illustrating a die-casting apparatusfor fabricating a vehicle part casing according to an embodiment in thepresent disclosure.

As illustrated in FIGS. 1 to 4, a die-casting apparatus for fabricatinga vehicle part casing according to an embodiment of the presentdisclosure fabricates the vehicle part casing, such as a differentialgear casing, using a molten aluminum (Al) alloy. The die-castingapparatus includes a fixed mold 100, a movable mold 200 movable in adirection of the fixed mold 100 to define a cavity C, and an exhaustingpart 300 lowering the internal pressure of the cavity C by evacuating aninterior of the cavity C.

The fixed mold 100 has a negative shape of one side of a vehicle partcasing carved thereinto, and is engaged with a fixed end to beconstantly fixed during a die-casting operation. In a certainembodiment, a gradient angle may be applied to a surface of the fixedmold 100 that performs sliding engagement with the movable mold 200 suchthat a completed die-cast vehicle part casing can be removed.

The movable mold 200 is movably disposed while being detachably attachedto the fixed mold 100, and has a positive shape of another side of thevehicle part casing carved in relief. The movable mold 200 is engagedwith a movable end, such that the movable mold 200 moves in thedirection of the fixed mold 100 during the die-casting operation. Themovable mold 200 is brought into close contact with the fixed mold 100,thereby defining the cavity C having a vehicle part casing shape betweenthe fixed mold 100 and the movable mold 200.

In addition, when the die-casting operation is completed, the movablemold 200 is detached from the fixed mold 100, and the vehicle partcasing molded within the cavity C is separated and discharged from thecavity C using a push pin.

The movable mold 200 has a plurality of first gas outlets 220 and aplurality of second gas outlets 230, through which gas contained in themolten Al alloy is exhausted. The plurality of second gas outlets 230communicate with the exhausting part 300.

In addition, the movable mold 200 has a first gas path 221 and a secondgas path 231 connecting the plurality of first and second gas outlets220 and 230 to the cavity C. In a certain embodiment, a diameter of theplurality of second gas outlets 230 is greater than that of theplurality of first gas outlets 220.

Thus, the amount of gas exhausted through the plurality of second gasoutlets 230 may be greater than the amount of gas exhausted through theplurality of first gas outlets 220.

In a certain embodiment, a distance between adjacent second gas outlets230 of the plurality of second gas outlets 230 increases in a directionaway from the cavity C. Therefore, a molten alloy path expands in adirection towards a downstream portion in which gas is exhausted,thereby improving gas exhausting ability.

A pressure sensor 240 may be connected to one of the plurality of firstgas outlets 220 in order to detect the degree of vacuum within thecavity C.

Here, the movable mold 200 has a detection block which communicates withthe corresponding first gas outlet 220 and on which the pressure sensor240 being disposed. The pressure sensor 240 is detachably attached tothe detection block, and the detection block may be opened and closed.

The exhausting part 300 is disposed at a downstream of the plurality ofsecond gas outlets 230 in a direction in which gas flows, such that theexhausting part 300 communicates with the plurality of second gasoutlets 230. The exhausting part 300 may evacuate gas contained in themolten Al alloy by forming a vacuum by lowering the internal pressure ofthe cavity C. For example, the exhausting part 300 may include a vacuumpump, a vacuum block, a vacuum valve, a vacuum hose, and the like thatare commonly used in, for example, a high-vacuum die-casting method.

In particular, the exhausting part 300 is implemented as an exhaustpassageway including a plurality of bent exhaust paths formed in avacuum block. Due to the bent exhaust paths of the vacuum valve, theexhausting part 300 functions as a cooling block through which themolten alloy is cooled. The exhausting part 300 can reduce castingpressure while reducing the amount of residual gas during thedie-casting process, thereby increasing life of the die-castingapparatus including the molds.

Here, the movable mold 200 has exhaust channels connecting the pluralityof second gas outlets 230 to the exhausting part 300. The exhaustchannels extend in bent shapes, through which gas is exhausted from theplurality of second gas outlets 230 by the exhausting part 300.

FIG. 5 is a view illustrating a sleeve part according to an embodimentin the present disclosure.

As illustrated in FIG. 5, the die-casting apparatus for fabricating avehicle part casing according to the present disclosure further includesa sleeve part 400 connected to a molten metal path 210 to supply amolten Al alloy to the cavity C.

Here, the sleeve part 400 has a gas outlet 410 at an upstream portion ina direction in which the molten Al alloy flows, such that gas within thesleeve part 400 can be naturally exhausted in a low-speed pouringsection. The gas outlet 410 may be configured to be opened and closed.

According to the present disclosure, the gas, which occurs during theprocess of pouring the molten Al alloy inside the sleeve part 400, canbe exhausted into the cavity C, thereby improving quality of a vehiclepart casing fabricated thereby. Here, the molten Al alloy may be pouredinto a lower part of the cavity C.

In addition, one side of the molten metal path 210 is connected to thesleeve part 400 and another side of the molten metal path 210 isconnected to the cavity C. The other side of the molten metal path 210connected to the cavity C may be divided into a plurality of pathsconnected to the cavity C. The other side of the molten metal path 210may be connected to lower part of the cavity C.

FIG. 6 is a flowchart illustrating a method of fabricating a vehiclepart casing using a die-casting apparatus according to an embodiment inthe present disclosure.

As illustrated in FIG. 6, a method of fabricating a vehicle part casingusing a die-casting apparatus includes a preparation step S1, a moldpreheating step S2, a molding step S3, a surface treatment step S4, anda finishing step S5.

In the preparation step S1, a molten Al alloy is prepared by heating andmelting an Al alloy, and a temperature of the molten Al alloy ismaintained in the range from 645° C. to 665° C.

In a certain embodiment, the composition of the Al alloy includes 88.2%to 80.3% Al, 9.6% to 12.0% Si, 1.5% to 3.5% Cu, 0.1% to 0.5% Mn, 0.1% to0.3% Mg, 0.1% to 0.5% Ni, 0.1% to 0.9% Fe, 0.1% to 0.5% Ti, 0.1% to 1.0%Zn, 0.1% to 0.3% Sn, 0.0% to 0.1% Pb, 0.0% to 0.1% Cr, and theinevitable impurities, based on 100% by weight of the alloy composition.According to the Al alloy having the above-defined composition, thecontent of Al is reduced, the content of Si is increased, and smallamounts of Ni, Ti, Sn, Cr, and the like are added, whereby the weight ofa fabricated vehicle part casing can be reduced and supporting strengthof the vehicle part casing can be improved.

FIGS. 7A-7F are a series of images illustrating defects formed when avehicle part casing was fabricated using molten Al having a temperaturebelow 645° C., and FIG. 8 is an image illustrating defects formed when avehicle part casing was fabricated using molten Al having a temperatureabove 665° C.

As illustrated in FIGS. 7 and 8, when a temperature of a molten Al alloywas less than 645° C., flowability of the molten Al alloy was decreased.In the process of pouring the molten Al alloy into the cavity C,premature solidification and an inaccurately-molded surface occurred,thereby deteriorating quality of a fabricated vehicle part casing. Whenthe temperature of a molten Al alloy was above 665° C., the amount offuel consumed was increased, thereby increasing fabrication costs.Localized heating occurred on a die-casting mold, thereby decreasing thelife of the die-casting mold. In a certain embodiment, the temperatureis limited to the range from 645° C. to 665° C.

FIGS. 9A and 9B are a series of images illustrating a fractured surfaceof a vehicle part casing fabricated according to an example in thepresent disclosure.

As illustrated in FIG. 9, in the present example, an Al alloy was heatedto 660° C. to melt, and the molten Al alloy was maintained at thistemperature. When the molten Al alloy was maintained at the temperatureof 660° C., a vehicle part casing having fine microstructures anduniform fractured surfaces was fabricated.

In the mold preheating step S2, a die-casting mold including a fixedmold 100 and a movable mold 200 is preheated prior to pouring a moltenAl alloy into the die-casting mold. The die-casting mold is preheated toa temperature ranging from 220° C. to 250° C.

FIG. 10 is an image illustrating surface voids formed when a vehiclepart casing was fabricated using a die-casting mold preheated to atemperature below 220° C. according to an example in the presentdisclosure, FIG. 11 is an image illustrating hit checks formed in adie-casting mold preheated to a temperature above 250° C. according toan example in the present disclosure, and FIG. 12 is an imageillustrating shrinkage defects when a vehicle part casing was fabricatedusing a die-casting mold preheated to a temperature above 250° C.according to an example in the present disclosure.

As illustrated in FIGS. 10 to 12, when the die-casting mold waspreheated to a temperature below 220° C., a temperature difference of400° C. or higher occurred between the die-casting mold and the pouredmolten Al alloy. Thus, the poured molten Al alloy was caused to beprematurely solidified, thereby deteriorating formability and causingshrinkage cracks defects in a product and due to a release agent. Whenthe die-casting mold was preheated to a temperature above 250° C., aprolonged period of time was required to cool the molten Al alloy afterpouring the molten Al alloy into the die-casting mold. This mayconsequently increase a working time, thereby degrading productivity.During solidification of the molten Al alloy, shrinkage defectsoccurred, and the degree of dimensional accuracy was decreased. Inaddition, deteriorations in the die-casting mold may rapidly occur,thereby reducing the longevity of the mold. Thus, in a certainembodiment, a temperature is limited to the range from 220° C. to 250°C.

In the present example, the temperature of the die-casting mold waspreheated at a temperature of 250° C.

The molding step S3 according to the present disclosure is a process ofpouring the molten Al alloy into the cavity C, and includes amold-closing step, a molten Al alloy-pouring step, a mold-opening step,and a mold-cleaning step.

In the mold-closing step, the fixed mold 100 and the movable mold 200 ofthe die-casting apparatus for fabricating a vehicle part casing areengaged such that the fixed mold 100 and the movable mold 200 are inclose contact with each other, thereby defining the cavity C between thefixed mold 100 and the movable mold 200. In the mold-closing step, aninsert core and a slide core are fitted into the die-casting mold.

The molten Al alloy-pouring step is a step of pouring the molten Alalloy into the cavity C defined between the fixed mold 100 and themovable mold 200. The molten Al alloy fed into the sleeve part 400 ispoured into the cavity C using, for example, a plunger, such as apiston. Here, the molten Al alloy may be poured into the lower part ofthe cavity C.

Here, a discharge tip positioned at a distal end of the sleeve part 400moves forwards at a speed of 0.2 m/s. After the discharge tip passes bythe inlet of the molten Al alloy, an interior of the sleeve part 400turns into an airtight state. Thus, in order to prevent gas within thesleeve part 400 from entering the cavity C to cause defects in aproduct, the gas outlet 410 having a diameter of 30 mm is opened toenable natural ventilation. Here, the gas outlet 410 is formed on anupper part of the sleeve part 400, within the range of 300 mm from astarting point of the plunger.

In a certain embodiment, a pouring pressure, i.e. a casting pressure, ofthe molten Al alloy ranges from 90 MPa to 110 MPa. When the pouringpressure is less than 90 MPa, flowability of the molten Al alloy isdegraded, which prolongs a period of time for pouring the molten Alalloy, thereby lowering productivity. When the pouring pressure isgreater than 110 MPa, the flowability of the molten Al alloy may beimproved. However, the molten Al alloy flows backwards due tocharacteristics of a dipper cup having an axially symmetrical and radialshape, thereby causing voids.

In a certain embodiment, the interior of the cavity C has a degree ofvacuum ranging from 140 mbar to 160 mbar. This range may obtain denseinternal structures from the Al alloy poured in the cavity C, therebyincreasing the density thereof. In addition, this range satisfiesmechanical characteristics required for the fabricated vehicle partcasing.

In the present example, the degree of vacuum within the cavity wasmaintained at 150 mbar while the casting pressure was maintained at 100MPa.

In the mold-opening step, a fabricated vehicle part casing is removed byseparating the movable mold 200 from the fixed mold 100 after thevehicle part casing is molded by cooling the molten Al alloy which isfilled in the cavity C. After the mold is cooled for a predeterminedperiod of time and the insert core and the slide core are removed, thevehicle part casing is removed.

In the mold-cleaning step, the fixed mold 100 and the movable mold 200are cleaned for the subsequent operation after the vehicle part casingis removed. Here, after first cleaning, a release agent is applied toinner surfaces of the mold, and second cleaning is performed.

The surface treatment step S4 is a step of trimming the removed vehiclepart casing. Runners or overflows and vent holes attached to an exteriorof the vehicle part casing are removed therefrom on a trimming die.

When the surface treatment on the vehicle part casing is completed, thefinishing step S5 is performed. In the finishing step S5, a workermanually removes burs having a size less than 2 mm, residing on surfaceof the vehicle part casing, using a manual tool, such as a grinder.

The vehicle part casing from which burs are removed is then subjected tovisual inspection before being shipped.

As set forth above, the present disclosure is directed to preheating thedie-casting mold after melting an Al alloy. It is thereby possible toimprove an operation of pouring a molten metal into a mold and to reducea period of time for cooling products, thereby improving workability ofproducts

In addition, each of the temperature of the molten Al alloy and thepreheating temperature of the die-casting mold is limited to apredetermined temperature range before the molten Al alloy is pouredinto the cavity from below. Thus, it is possible to maintain die-castingconditions due to the flowing characteristics of an Al alloy, therebyimproving denseness of fabricated vehicle part casings and reducing adefective rate thereof.

Furthermore, in an Al alloy, the content of Al is reduced, the contentof Si is increased, and a small amount of Ni, Ti, Sn, or Cr is added. Itis therefore possible to reduce the weight of the Al alloy and improvethe supporting strength thereof.

In addition, the die-casting mold is implemented as a vacuum die-castingmold. It is therefore possible to exhaust gas contained in the molten Alalloy and reduce the amount of gas residing in the cavity in order toreduce voids formed in die-cast products, thereby improving fabricationefficiency.

Although the exemplary embodiments in the present disclosure have beendescribed for illustrative purposes, a person skilled in the art willappreciate that various modifications, additions, and substitutions arepossible, without departing from the scope and spirit of the presentinvention as disclosed in the accompanying claims.

What is claimed is:
 1. A method of fabricating a vehicle part casingusing a die-casting apparatus, comprising: preparing a molten aluminum(Al) alloy by heating an Al alloy; preheating a die-casting mold;molding the vehicle part casing by pouring the molten Al alloy into thedie-casting mold; removing the vehicle part casing from the die-castingmold and trimming a surface of the vehicle part casing; and removingburs on the vehicle part casing.
 2. The method according to claim 1,wherein the step of preparing the molten Al alloy comprises heating theAl alloy at a temperature ranging from 645° C. to 665° C.
 3. The methodaccording to claim 1, wherein the step of preheating the die-castingmold comprises preheating the die-casting mold at a temperature rangingfrom 220° C. to 250° C.
 4. The method according to claim 1, wherein thestep of molding the vehicle part casing comprises pouring the molten Alalloy to a lower part of the die-casting mold.
 5. The method accordingto claim 4, wherein the step of pouring the molten Al alloy into thedie-casting mold comprises pouring the molten Al alloy at a pressureranging from 90 MPa to 110 MPa while maintaining an internal vacuumpressure of a cavity in the die-casting mold in a range from 140 mbar to160 mbar.
 6. The method according to claim 1, wherein a composition ofthe Al alloy comprises 88.2% to 80.3% Al, 9.6% to 12.0% Si, 1.5% to 3.5%Cu, 0.1% to 0.5% Mn, 0.1% to 0.3% Mg, 0.1% to 0.5% Ni, 0.1% to 0.9% Fe,0.1% to 0.5% Ti, 0.1% to 1.0% Zn, 0.1% to 0.3% Sn, 0.0% to 0.1% Pb, 0.0%to 0.1% Cr, and inevitable impurities, based on 100% by weight of thealloy composition.
 7. The method according to claim 1, wherein the stepof molding the vehicle part casing comprises molding the vehicle partcasing while exhausting gas from the molten Al alloy using vacuum. 8.The method according to claim 1, wherein the die-casting mold includes afixed mold and a movable mold, in which the fixed mold has a negativeshape so that one side of the vehicle part casing is carved thereintoand the movable mold has a positive shape so that another side of thevehicle part casing is carved thereinto.
 9. A die-casting apparatus forfabricating a vehicle part casing comprising: a fixed mold having anegative shape so that one side of the vehicle part casing is carvedthereinto; a movable mold disposed movable in a direction towards thefixed mold, the movable mold having a positive shape so that anotherside of the vehicle part casing is carved thereinto, in which themovable mold is engaged with the fixed mold between which a cavityhaving a shape of the vehicle part casing is formed; and an exhaustingpart connected to the cavity and decreasing an internal pressure of thecavity, in which the exhausting part exhausts gas contained in a moltenAl alloy which is inserted into the cavity.
 10. The die-castingapparatus according to claim 9, wherein the movable mold comprises: amolten metal path connected to a lower part of the cavity, so that amolten metal enters the cavity through the molten metal path; aplurality of first gas outlets formed in an upper part of the cavity, inwhich the gas is contained in the plurality of first gas outlets; and aplurality of second gas outlets connected to the exhausting part to forma vacuum in an interior of the cavity.
 11. The die-casting apparatusaccording to claim 10, wherein the movable mold has: first gas paths;and second gas paths connecting the plurality of first gas outlets andthe plurality of second gas outlets to the cavity, and wherein adiameter of each of the second gas paths is smaller than that of each ofthe first gas paths.
 12. The die-casting apparatus according to claim10, further comprising a pressure sensor connected to one first gasoutlet among the plurality of first gas outlets to measure the internalpressure of the cavity.
 13. The die-casting apparatus according to claim10, further comprising a sleeve part connected to the molten metal paththrough which the molten metal is poured, wherein the sleeve part has agas outlet in an upper part to exhaust the gas therefrom.